Why does Firefox's per-site process isolation (Fission) increase RAM usage exponentially on low-memory devices with 20+ tabs?

 but tabs reload constantly, disrupting workflow

 still high, confirming it's not extension-related

 "Web Content" processes, one per origin as expected with Fission

  without fully disabling site isolation? I found 
  dom.ipc.processCount but changing it doesn't seem to affect 
  Fission's per-origin process spawning behavior.

  and what is the safe range to modify it?

  it automatically consolidates processes — similar to Chrome's 
  memory saver — and if so, which about:config keys control it?

**Background:** I'm a senior software engineer running Firefox Developer Edition on a Linux machine with 8GB RAM. I have Fission architecture (site isolation) enabled, which I understand is now the default since Firefox 95+. **The problem:** When I open 20 or more tabs across different domains, Firefox's memory consumption scales dramatically — often reaching 4–6GB of RAM for what should be lightweight browsing sessions. This is significantly higher than what I observed before Fission was enabled. **What I've already tried:** - Disabled hardware acceleration → no significant improvement - Set browser.tabs.unloadOnLowMemory to true → partial relief but tabs reload constantly, disrupting workflow - Reduced content.notify.interval → marginal improvement - Tested with all extensions disabled (safe mode) → RAM usage still high, confirming it's not extension-related - Checked about:memory → large number of separate "Web Content" processes, one per origin as expected with Fission **What I'm trying to understand:** 1. Is there a way to set a maximum process count cap for Fission without fully disabling site isolation? I found dom.ipc.processCount but changing it doesn't seem to affect Fission's per-origin process spawning behavior. 2. Is browser.tabs.min-warm-process-count a relevant setting here and what is the safe range to modify it? 3. Does Firefox have a built-in memory pressure threshold where it automatically consolidates processes — similar to Chrome's memory saver — and if so, which about:config keys control it? **Environment:** - Firefox Developer Edition 151.0b10 - OS: Ubuntu 24.04 LTS - RAM: 8GB - Fission enabled: confirmed via about:support - Extensions: disabled for testing